Denture adhesives are employed for the purpose of assisting the adherence of dentures to the oral mucosa. Such adhesives are usually formulated either as anhydrous powders or as cream based formulations. Both types acquire moisture from saliva to hydrate the formulation in such a way to form a thin film between the denture and oral mucosa and to develop their useful properties. A high degree of tack is essential for the adhesive to function properly and equally important is the cohesive strength of the hydrated denture adhesive. A high degree of strength helps to prevent loss of adhesion of the denture to the oral mucosa.
Another important characteristic of a denture adhesive is the rate of hydration. Only after the adhesive becomes fully hydrated does it become fully effective. Not only do the polymers and/or gums employed play an important role in determining the rate of hydration but also the form of the adhesive is significant. Thus, for example, a powder adhesive can hydrate faster than a cream. The rate of hydration further affects the smoothness and overall mouth feel of the denture adhesive. Moreover, it is apparent that part of the adhesive will be between the denture and the gums and will therefore not have access to the moisture because it is out of direct contact with the saliva. It is therefore important that a denture fixative composition have the characteristic of becoming hydrated evenly throughout so that its strength is evenly distributed. As a result, various polymers and gums have been used heretofore for the specific purpose of promoting adhesion. While these hydration adjuvants may not contribute to the tack and strength of the denture adhesive, they are useful in assisting in water pick up.
Polyacrylic acid has been employed in numerous pharmaceutical formulations in order to exploit its thickening, suspending and emulsifying capabilities. It has been used also in denture adhesive formulations. For example, U.S. Pat. No. 4,373,036 teaches the use of polyacrylic acid with neutralizing agents and cross-linkers in a denture adhesive formulation which can also include hydroxypropyl cellulose and polyethylene oxide. However it cannot be used alone because, as is known, a partially or wholly neutralized polyacrylic acid generates a gel in aqueous systems which has a low cohesive strength and a structure which may easily be ruptured when subjected to stresses such as those which occur during mastication.
Polyvinyl alcohol is a water soluble polymer which can form a highly viscous gel in water. It has been used as a thickener, emulsifier, adhesive and coating. U.S. Pat. No. 4,880,702 teaches the use of polyvinyl alcohol in a three layer composition for stabilizing dentures alone or in combination with polyethylene oxide, sodium carboxymethyl cellulose or microcrystalline wax. The polyvinyl alcohol is cast into a thin film which is used in the outer layers of the composition and becomes tacky when hydrated in the mouth.
Polyalkylene oxides such as polyethylene oxide and polypropylene oxide have been widely used as solvents, lubricants, surfactants and in pharmaceutical and cosmetic bases. They have also been used in a denture adhesive composition containing, inter alia, cellulose ethers, an alkali metal salt of carboxymethyl cellulose and a hydrocarbon base (EP 140,486). Polyethylene glycol has been used in denture adhesives as taught for instance in U.S. Pat. Nos. 4,530,942, 4,522,956, 4,521,551, 4,514,528 and 4,474,902. Polypropylene glycol has been used in conjunction with polyvinyl acetate and other natural gums in U.S. Pat. No. 4,804,412.
Chang et al. in U.S. Pat. Nos. 4,470,814 and 4,542,168 teach a denture fixative composition containing as the fixative, a partially neutralized and crosslinked polyacrylic acid or a precursor combination of the polyacrylic acid, neutralizing agent and crosslinking agent adapted to form the active fixative, and at least one hydrophilic polymer which is preferably sodium carboxymethyl cellulose, hydroxypropyl guar or sodium alginate. The crosslinking agents are the dentally acceptable salts, oxides and bases of divalent cations and/or polyhydroxy compounds such as glycerin, propylene glycol, ethylene glycol, tetramethylene glycol and the like.
It is known that polyacrylic acid and compounds containing hydroxyl functionality interact. A combination of the two materials does result in a mixture with a higher viscosity than either of the compounds alone and when this occurs, a highly viscous and gummy material is obtained. That property is advantageous when the combination is used as a denture adhesive but the same property also introduces an element of difficulty in applying the denture adhesive onto the dentures. It is desirable that the denture adhesive be applied as a thin layer on the denture in order to provide for an even distribution of the adhesive and a comfortable fit. Development of a viscous and gummy consistency when the two compounds are mixed makes the even application of the denture adhesive more difficult.
It is accordingly the object of this invention to provide a new denture adhesive composition which hydrates more evenly, and develops high tack and superior cohesive strength and which can be more easily applied to a denture. This and other objects of the invention will become apparent to those of ordinary skill in this art from the following detailed description.